1. Field of the Invention
The present invention relates to an ultrasonic cleaning device for ultrasonically cleaning an object such as, for instance, a semiconductor wafer or an LCD glass plate.
2. Description of the Related Arts
A liquid processing method in which semiconductor wafers or LCD glass plates or the like are cleaned by being sequentially immersed in a processing tank containing a processing liquid such as treating liquid or rinsing liquid (cleaning liquid) is generally used in the manufacturing process of semiconductor manufacturing equipment.
An ultrasonic cleaning device is known which is shown in FIG. 16 and in which a plurality of vibrating plates (transducers) 3 are affixed using an adhesive to, for instance, the bottom of a cleaning tank 2 containing objects to be cleaned, for instance semiconductor wafers W (hereinafter wafers W), and cleaning liquid, for instance pure water 1. In this ultrasonic cleaning device, a high frequency voltage of, for instance, 200 KHz to 1 MHz generated by an oscillation source 4 is applied to each vibrating plate 3, thereby exciting the vibrating plates 3 and enabling particles deposited on the wafers W to be removed. The relation between particle removal rate (A) and sound pressure (B) is:
A.varies.T.times.B2 (T is a proportionality constant)
As the above equation demonstrates, the relationship between the excitement of the vibrating plates 3, namely sound pressure, and the particle removal rate is proportional, and therefore particles and the like deposited on wafers W can be removed by exciting the vibrating plates 3 and increasing sound pressure.
However, in a conventional cleaning device of this type, the vibrating plates 3 have to be separated for insulation because they are driven by oscillators 4 having independent oscillation sources, respectively. As a result, ultrasonic interference occurs in the gap created between the vibrating plates 3, producing unevenness in the sound pressure as shown in FIG. 17a. Consequently, there has been the problem that the particle removal rate has been uneven as shown in FIG. 17b, causing inconsistency in the cleaning.
As a means of solving this problem, an ultrasonic cleaning device has been proposed wherein a level difference is provided on the installation surfaces and the vibrating plates are installed on both sides of this level difference (See: Japanese Patent Laid-Open No. Hei 5-243203). However, even in the technology disclosed in Japanese Patent Laid-Open No. Hei 5-243203, the level difference between adjacent vibrating plates creates a gap which causes ultrasonic interference. This creates the problems that uniform sound pressure cannot be obtained and particles cannot be uniformly removed, causing inconsistencies in cleaning. There is an additional problem that, installing the vibrating plates with a level difference between installation surfaces requires precision during assembly and increases the complexity and scale of the device increases.